Surface hardening of titanium



3 ,268,372 Ce Patented August 23, 1966 3,268,372 SURFACE HARDENING F TITANIUM Peter Albert John Brotherton and Cyril Dawes, Wednesbury, England, assignors to Joseph Lucas (Industries) Limited, Birmingham, England No Drawing. Filed Sept. 9, 1963, Ser. No. 307,350 Claims priority, application Great Britain, Sept. 12, 1962, 34,801/ 62 4 Claims. (Cl. 148-20) The object of this invention is to provide a convenient method of hardening the surface of titanium.

A method in accordance with the invention comprises heating the titanium in a fused salt mixture of potassium and/or sodium cyanide and cyanate at a temperature in the range of 550 C. to 800 C. so as to form a surface layer of titanium combined with nitrogen and oxygen, and maintaining the temperature within said range for sifiicient time to form a surface layer of the required depth.

It is found that for temperatures in the range 550 C. to 650 C. a suitable mixture is 5% to of cyanate and 10% to 30% cyanide by weight. However, for temperatures in the range 650 C. to 800 C. the upper limit of the cyanate range can be increased to 30%. A typical period of time is between two and six hours.

In one example, titanium was heated to 700 C. and maintained at this temperature for four hours in a fused salt mixture containing by weight 25% sodium cyanide and 10% sodium cyanate, the remainder being alkaline earth metal carbonates, chlorides or oxides. The titanium was then cooled in air or by quenching. A hardened layer Was formed which was 0.0-0.4 inch thick and had a hardness of the order of 700 Hv.

Having thus described our invention what we claim as new and desire to secure by Letters Patent is:

1. A method of hardening the surface of titanium, comprising heating the titanium in a fused salt mixture of potassium land/or sodium cyanide and cyanate at a temperature in the range of 550 C. to 800 C. so as to form a surface layer of titanium combined with nitrogen and oxygen, and maintaining the temperature within said range for sufiicient time to form a surface layer of the required depth.

2. A method as claimed in claim 1 in which the temperature is in the range 550 C. to 650 C., the cyanate range is from 5% to 10% by weight, and the cyanide range is from 10% to 30% by weight.

3. A method as claimed in claim 1 in which the temperature is in the range 650 C. to 800 C., the cyanate range is from 5% to 30% by weight, and the cyanide range is from 10% to 30% by Weight.

4. A method as claimed in claim 1 in which said time is between one and twenty four hours.

References Cited by the Examiner UNITED STATES PATENTS 2,453,896 11/1948 Dean 1486.11 2,892,743 6/1959 Griest et a1 148-315 X 2,927,875 3/1960 Muller 148l5.5

DAVID L. RECK, Primary Examiner.

C. N. LOVELL, Examiner. 

1. A METHOD OF HARDENING THE SURFACE OF TITANIUM, COMPRISING HEATING THE TITANIUM IN A FUSED SALT MIXTURE OF POTASSIUM AND/OR SODIUM CYANIDE AND CYANATE AT A TEMPERATURE IN THE RANGE OF 550*C. TO 800*C. SO AS TO FORM A SURFACE LAYER OF TITANIUM COMBINED WITH NITROGEN AND OXYGEN, AND MAINTAINING THE TEMPERATURE WITHIN SAID RANGE FOR SUFFICIENT TIME TO FORM A SURFACE LAYER OF THE REQUIRED DEPTH. 